The electrocardiogram (ECG or EKG) is recognized as one of the most successful and important tools for rapid, noninvasive assessments of cardiac conditions. The resting 12-lead ECG (standard 12-lead ECG) recordings have been used to determine cardiac conditions in the presence of conflicting or ambiguous clinical symptoms. A 12-lead ECG can be obtained by attaching 10 electrodes to a patient: 4 limb lead electrodes are attached to limbs (left and right wrist, left and right ankle) and 6 precordial lead electrodes are attached to the torso. This configuration allows for recording leads I, II, Vi leads (where i=1 to 6), and calculating leads III, aVR, aVL and aVF. Electrocardiographs can be used to display/print ECG waveforms and for generating clinical statements based on diagnostic criteria derived from ECG measurements. Interpretation of an ECG is performed by electrocardiogram waveform analysis and can sometimes be performed by a serial comparison of a current ECG to a previously recorded ECG.
However, the resting 12-lead ECG obtained in the hospital or doctor's office can have limitations imposed by the recording environment. Everyday life, exercise, stress and a number of physiological conditions can elicit cardiac problems that can be masked or are not present during recordings on the human body at rest. Therefore, a stress test and ambulatory recordings can be used as additional sources of information on cardiac status. During a stress test, limb electrodes can be moved to the torso to reduce noise and artifacts caused by movement of long wires, muscle activity, and unstable electrode-skin interface.
Moreover, the acquisition of cardiac signals from a patient while in a non-hospital setting can be hampered by a variety of circumstances. To obtain high-quality ECG recordings, the electrode-skin interface needs to be stable, otherwise noise and artifacts can distort the recording of signals. Furthermore, in some situations, it is impractical to attach electrodes and wires to the body of a patient in motion. In ambulatory settings, it can be impractical to record with a large number of wires, so a small recorder can be used to record only a few ECG channels.